Thermionic tubes



W. H. HUNTER THERMIONIC TUBES Filed Sept. 30, 1954 Feb. 3, 1959 lNlENTOR WINDSOR H. HUN TEI? THERMIONIC TUBES Windsor H. Hunter, Anbumdale,Mass., asslgnor to Raytheon Manufacturing Company, Waltham, Mass., acorporation of Delaware Application September 30, 1954, Serial No.459,359

1 Claim. (Cl. 313-260) This invention relates to thermionic tubes andmore specifically to such tubes constructed so as to resist vibrationand reduce the microphonics in their output.

Therrnionic tubes, when subjected to vibrations as in aircraft, producea type of noise called microphonics due to movement of tube elementswith respect to each other. The movement of a grid, particularly thecontrol grid with reference to the other tube electrodes, particularlythe cathode, is most likely to cause such microphonic noise as it iswell known that the distance between the grid and cathode is animportant factor in determining the characteristics of the tube,particularly its transconductance. The problem is to provide stiffeningfor a grid without affecting the operation of the tube adversely and inas inexpensive a way as possible.

In the present invention this is accomplished by mounting stakes in boththe upper and lower mica spacers on either side of the grid supports andwelding a metal strip between each stake and its associated gridsupport. A strip of metal is also attached to the outside of each gridsupport. Great improvement in the operation of tubes constructed in thisway is obtained over tubes of the same type not having thisconstruction. This improvement is obtained with only a small increase inthe cost of production.

Other and further advantages, objects, and features of the inventionwill be better understood from the following description taken inconjunction with the accompanying drawing, wherein:

Fig. 1 is an enlarged longitudinal sectional view partly broken away ofa tube made according to the invention;

Fig. 2 is a further enlargement of a portion of the tube shown in Fig.1; and

Fig. 3 is a section taken along the line 3-3 of Fig. 2.

In the drawing the reference numeral designates the envelope of the tubesealed with a button type seal 11. Although a button type seal is shownit is to be understood that the invention may be used with any type ofseal. An indirectly heated cathode 12 is inserted in openings in twospacers 13 and 14 which are usually made of mica. The cathode 12 isconnected through a conductor 15 that passes through the seal 11 to theexternal circuit. A heater (not shown) is mounted within the cathode 12and connected to the external circuit through conductor 16. An anode 17is mounted about the cathode 12 between the spacers 13 and 14 on twosupports 18 and 20. A grid 21 is formed with a wire 22 wound about twosupport rods 23 and 24. The wire 22 is swaged into notches formed in thesupport rods 23 and 24. Four stakes 25, 26, 27, and 28 are mounted onenear each end of the grid support rods 23 and 24. Two of these stakes 27and 28 are mounted in the spacer 14 from below and two such stakes 25and 26 are mounted in the upper spacer 13 from above. A short metalstrap 30 is welded or otherwise attached to the support rod 23 and thestake 25. A second such strap 31 is welded to the support rod 24 and tothe stake 26. A similar short metal strap 32 is welded to the supportrod 23 and the stake 27 which also acts as the connector to the outsidecircuit through the seal 11. A similar short strap 33 is welded to thesupport rod 24 and the stake 28 which also acts as the connector to theoutside circuit through the seal 11. The bottom stakes need notnecessarily form a part of the electrical circuit; they may be usedsolely as additional mechanical support as are the top stakes 25 and 26as shown in Figs. 1 and 2. The added stakes 25, 26, 27, and 28 and theconnecting straps 30, 31, 32, and 33 serve to give additional support tothe grid 21 in the plane of thesupport rods 23 and 24. In addition ametallic ribbon 34 or 35 is attached to each of the support rods 23 and24 on their outer surfaces. These ribbons 34 and 35 are shown as beingformed with an inward curve. This inward curve is desirable but notnecessary. These ribbons serve to reduce the movement of the grid 21from one side to the other of the original plane of the support rods 23and 24. The mount structure of the tube is completed by a getter 36 ofany of the well-known types supported on and electrically connected tothe anode 17.

The structure resulting from this construction resists distortion due tovibration because the addition of the ribbons to the support rodsincreases the resonant frequency of the rods by increasing the stiffnessto mass ratio and so greatly reduces the production of microphonics inthe output of a tube made in this way. In a representative tube type theconstruction of this invention reduced the microphonic output underwhite noise vibration by a factor of 56 and the microphonic output with40 cycles per second vibration at an intensity of 15 Gs was reduced by afactor of 44. This considerable improvement was obtained at a smalladditional production cost.

This invention is not limited to the particular details of construction,materials and processes described, as many equivalents will suggestthemselves to those skilled in the art. It is accordingly desired thatthe appended claims be given a broad interpretation commensurates withthe scope of the invention within the art,

What is claimed is:

Support means for a grid in a thermionic device comprising a pair ofrods, a pair of dielectric spacers into which the rods are inserted anda strip of metal attached to the outside of each rod between the spacersand extending to either side beyond the rod.

References Cited in the file of this patent UNITED STATES PATENTS WalshApr. 17, 1951

